1. Field of the Invention
The present invention generally relates to a method for forming a low dielectric film in an interconnect structure and more particularly to a method for improving the moisture absorption of porous low dielectric film.
2. Description of the Prior Art
Through advanced semiconductor process in techniques, integrated circuit devices with sub-micron and sub-half-micron features sizes can now be manufactured. This trend toward deep sub-micron technology (i.e., involving feature sizes less than 0.35 microns) has, in turn, driven the need for multilevel interconnect. As a result, circuit performance in the deep sub-micron regime is increasingly a function of the delay time of electronic signals traveling between the millions of gates and transistors presented on the typical integrated circuit chip. Parasitic capacitance and resistance effects resulting from these otherwise passive interconnect structures must therefore be well controlled. Toward this end, recent researches emphasize the use of low resistance metals (e.g., copper) in conjunction with insulating material with low dielectric constant (low-k dielectrics) between metal lines. Low-k dielectric meaning that is a dielectric material, which exhibits a dielectric constant substantially less than conventional dielectric materials such as silicon dioxide, silicon nitride, and silicon oxynitride. Silicon dioxide, for example, has a dielectric constant than 4.1. Copper is desirable in that its conductivity is relatively high and it is relatively high resistance of electromigration than many metals (for example, aluminum).
On the other hand, considerable attention has been focused on the replacement of silicon dioxide with new materials, i.e. particular materials having lower dielectric constants, since both capacitive delays and power consumption depend on the dielectric constant of the insulator. Accordingly, circuit performance enhancement is need for combining the copper conductors with low dielectric constant insulators (k less than approximately 4).
Herein, low dielectric constant material means a material having a dielectric constant lower than about 3.5, preferably lower than 3 and most preferably about 2 or even lower. Unfortunately, materials with a lower dielectric constant have characteristics that make them difficult be integrated into existing integrated circuit structures and processes. Many polymeric materials such as polysilsesquioxane, parylene, polyimide, benzocyclobutene, and amorphous Teflon have lower dielectric constants (lower permittivities). On the other hand, for inorganic materials, Aerogel having porous silica structure which are typically made from a gelation of tetraethoxysilane (TEOS) stock solution. Compared to conventional SiO2, these preferred low-k materials due to the nature of structure typically have low mechanical strength, poor dimensional stability, poor temperature stability, high moisture absorption, permeation, poor adhesion, large thermal expansion coefficient, and an unstable stress level. Because of these characteristics, the use of polymer or other low dielectric materials as the only replacement for SiO2 in integrated circuit processes or structures is very problematic.
In the conventional technique, after plasma etching process or chemical mechanical polishing (CMP) process, the plasmas process with hydrogen gas is provided a plurality of hydrogen atoms on the surface of porous low-k dielectric film to form hydrophobic Sixe2x80x94H bond on surface of porous low-k dielectric film. However, the plasma process is also used to etch the porous low-k dielectric film to bring about the plasma damage of porous low-k dielectric film.
Furthermore, there is a solution chemical reaction method to replace the prior art technique to form hydrophobic protection film and the plasma damage of porous low-k dielectric film will not be created.
It is an object of this invention is to provide a hydrophobic film to improve the absorption moisture of porous low-k dielectric film after plasma etching process or chemical mechanical polishing process.
It is another object of this invention is to maintain the dielectric constant of porous low-k dielectric film and the leakage current is reduced.
It is still another object of this invention is to provide a low temperature, a simple manufacture process and the low cost for fabrication.
In this invention, after plasma process or chemical mechanical polishing process, the wafer is placed in the supplementary instrument such as ultrasonic vibration apparatus or reflux apparatus with reactive solution such as dihydrosiloxane reagent (H2Si(OH)2 or H2Si(OR)2) or organosiloxane reagent (H2Si(OH)2 or H2Si(OR)2, wherein R is alkyl group, Rxe2x95x90CH3, C2H5, C3H7) with concentration about 10 wt % to 20 wt %, and a dilute inorganic acid solution such as H2SO4 (sulfuric acid), HCl (hydrochloric acid), or HNO3 (nitric acid) is serve as catalyst in this invention. After five to ten minutes, the reaction is completely, the hydrophobic protection film (Sixe2x80x94Oxe2x80x94SiR2) is formed on surface and sidewall of porous low-k dielectric film to improve the moisture absorption of porous low-k dielectric film and the leakage current is reduced in subsequently processes.